Copper Slag Blended Cement : An Environmental Sustainable Approach for Cement Industry in India

Indian cement industry is facing environmental issue of emission of carbon dioxide (CO2), a greenhouse gas. Blended cements including supplementary cementitious materials are substitute of Portland cement to reduce CO2 emission. The present paper investigates the appropriateness of copper slag (CS) as supplementary cementitious material. Strength properties and hydration of mixes were determined at different replacement levels of CS with cement. Compressive, flexural and tensile strength of each mix was found out at different curing periods. The hydration of cement was investigated through X-ray diffraction (XRD). The strength test results showed that substitution of up to 20% of CS can significantly replace Portland cement. XRD test results were corresponding to strength test results. The present study encourages the utilization of CS as supplementary cementitious material to make economical and environmentally sustainable blended cement.


IntrODuCtIOn
Cement industry is the fastest growing industry in India.As per the economic advisor, Department of Industrial Policy & Promotion (DIPP), during the year 2013-14 in India, cement production was 255.57 million tons.But, cement industry has facing many environmental issues.The main environmental issue associated with cement industry is emission of carbon dioxide (CO 2 ), a greenhouse gas.Cement industry generates significant amount of CO 2 .Producing a ton of Portland cement generates nearly a ton of CO 2 1 .Currently, large production of Portland cement in India releases large amount of CO 2 to environment.Supplementary cementitious materials are substitute of Portland cement to reduce CO 2 emission.These materials replace some amount of Portland cement, without affecting its mechanical properties.Different industrial wastes likes slag and metakolin can exercise as supplementary cementitious materials 2 .Portland cement which includes supplementary cementitious material is blended cement.
CS is a waste material generates from refining of copper, and may have the potential to be used as supplementary cementitious materials in cement industry 3 .In India approximately six million tons of CS generates annually 4 .Various investigations have been carried out to determine the suitability of CS as a partial replacement of cement.These investigations showed that CS as cement replacement exhibited better strength and long-term properties as compare to normal concrete batches [5][6][7][8][9] .However, in India, studies regarding exercise of CS in cement industry are rarely seen in literature.Therefore, in this study an attempt is made to determine the appropriateness of CS as supplementary cementitious material for the production of environmentally sustainable blended cement.

Cement
Ordinary Portland cement of 43 grade was used in this study.All properties of Ordinary Portland cement conformed to BIS 8112 10 .

Fine and coarse aggregates
The fine aggregates used were river sand having a 4.75 mm nominal maximum size.The coarse aggregate used were crushed stone having a 20 mm nominal maximum size.Specific gravity of fine and coarse aggregates calculated as per BIS 2386 11 was 2.64 and 2.60 respectively.Fine aggregates conformed to grading zone II as per BIS 383 12 .The grading requirement of coarse aggregates was in accordance with BIS 383 12 .

Copper slag (CS)
CS obtained from Synco Industries Limited (Jodhpur, Rajasthan) was used in this study.CS was black in color and irregular in shape.Specific gravity of CS was 3.51.It was ground in to fine powder and sieved below 90 micron sieve to attain similar fineness as cement.Fineness of CS determined as per BIS 4031 13 using Blaine' specific surface area method was 325 m 2 /kg.The chemical properties of CS are given in Table 1.

mEthODS mix proportions and sample preparation
In this study, the one reference mix C1 was designed according to BIS 10262 14 as plain concrete.Further four mixes were prepared other than reference mix at different replacement levels of copper slag (5%, 10%, 15% & 20%) with cement.Mix proportions of concrete mixes are given in Table 2.The quantities of cement, coarse aggregates, fine aggregates, copper slag and water for each mix were weighed separately.The cement and copper slag were mixed dry.Fine aggregates were mixed to this mixture in dry form.The coarse aggregates were mixed to get uniform distribution throughout the batch.Water was added to the mix and then mixed thoroughly for 3 to 4 minutes in a proper mechanical mixer.

testing procedure
The compressive and split tensile strength of each mix was found out from cube specimens of 150 mm X 150 mm X 150 mm in size.The flexural strength of each mix was calculated from prism specimens of 150 mm X 150 mm X 700 mm in size.The compressive and flexural strength of specimens was tested according to BIS 516 15 .The splitting tensile strength of specimens was tested according to BIS 5816 16 .All strength tests were performed on universal testing machine after 7, 28 and 90 days of curing.

hydration study using XrD
The degree of hydration of cement was investigated by XRD.The diffracted peaks of different hydration products can be found out using XRD.The degree of hydration of cement can be observed from these diffracted peaks.The intensity of these diffracted peaks plotted against the diffraction angle 2è (degrees).The intensity was measured in counts per second (cps).The X-ray diffraction test was performed on samples of cementitious powder of mixes with blends; C1 (0% CS), C3 (10% CS) and C5 (20% CS).The samples of cementitious powder were collected from the remnant of concrete specimens after 28 and 90-days compressive strength test.The X-ray diffractograms of different samples were recorded on Panalytical X'Pert PRO with Bragg-Brentano geometry.Powder samples were loaded

Compressive strength
The average 7 th , 28 th and 90 th day compressive strength of different mixes are given in Table 3 and shown in Fig. 1.The results show that, 7 and 28 day compressive strength of concrete is decreased with increase in CS content in mix due to non cementitious properties of CS.The small quantity of CaO in CS (Table 1) does not possess any cementitious properties.Thus CS does not bind the mix; it disperses the mix and reduces the compressive strength of concrete.However, the 90 day compressive strength of concrete is increased with increase in CS content in mix (Fig. 1).The presence of SiO 2 in CS (Table1), initial the pozzolanic reaction and increased the compressive strength.At higher percentage of CS (20% CS), the compressive strength increased from 28.30 MPa at the 28 th day to 47.93 MPa at the 90 th day (Table 3).At the 90 th day, 20% of CS showed maximum compressive strength of 47.93 MPa.It is noted that strength gain took place after 28 th day curing due to initiate of pozzolanic reactions of CS.The compressive strength test results showed that up to 20% of CS significantly replace Portland cement and provides environmental sustainable blended cement.

Flexural and splitting tensile strength of concrete
The average 7 th , 28 th and 90 th day flexural strength of different concrete mixes are given in Table 3 and shown in Fig. 2. The average 7 th , 28 th and 90 th day splitting tensile strength of different concrete mixes are given in Table 3 and shown in Fig. 3.The results show that, 7 th and 28 th day flexural and splitting tensile strength of concrete is decreased

Fig. 3 :
Fig. 3: Average 7 th , 28 th and 90 th day splitting tensile strength of different concrete mixes